you need to be carefull with cheapo ones, theyre prone to well... blowing up. make sure you get the connections the correct way round or it will blow up lol. (I have done it before)
Yes IMAX B6s are good but umm is it genuine? I've seen them on Cool Components for £30 and was just looking at a WE charger for £16 so was thinking the IMAX can't be cheaper than that.
I use an IMax B6 to and they are great. If you want to check that it is a real one when you buy it there should be a silver sticker on it, peel it back and enter the code onto the Imax Website and it will say if it is real or not.